Architecture for Chaining Legacy Layer 4-7 Service Functions
draft-dunbar-sfc-legacy-l4-l7-chain-architecture-03
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| Last updated | 2014-02-10 | ||
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draft-dunbar-sfc-legacy-l4-l7-chain-architecture-03
Network working group L. Dunbar
Internet Draft Huawei
Intended status: Informational Ron Parker
Expires: August 2014 Affirmed Networks
I. Smith; S. Majee
F5 Networks
N. So
Tata Communications
Donald Eastlake
Huawei
February 10, 2014
Architecture for Chaining Legacy Layer 4-7 Service Functions
draft-dunbar-sfc-legacy-l4-l7-chain-architecture-03.txt
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Abstract
This draft describes the architecture for chaining existing L4-L7
service functions that don't have Layer 2-3 switching/routing
capability and are not aware of newly defined service encapsulation
layer. The intent is to identify optimal architecture for flexibly
chaining existing Layer 4-7 functions to meet various service needs.
Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................3
3. Legacy Layer 4-7 Service Functions and Chaining................4
3.1. Layer 4-7 Service Functions...............................4
3.2. Service Functions Chaining for Wireless network...........4
4. Architecture for Chaining Legacy Layer 4-7 Service Functions...6
4.1. Service Function Forwarder for Layer 4-7 Service Functions6
4.2. L4-L7 nodes connection to SFF Nodes.......................7
4.3. Traffic Steering at SFF Nodes.............................8
5. Control Plane for L4-L7 Service Function Chain.................9
5.1. Multiple Instances of a Service Function..................9
5.2. Service Chain Classification.............................11
5.3. Layer 4-7 traffic Steering...............................13
6. Service Chain from the Layer 7 Perspective....................14
7. Conclusion and Recommendation.................................15
8. Manageability Considerations..................................15
9. Security Considerations.......................................15
10. IANA Considerations..........................................15
11. References...................................................15
11.1. Normative References....................................15
11.2. Informative References..................................15
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12. Acknowledgments..............................................16
1. Introduction
This draft describes the architecture for chaining existing L4-L7
service functions that don't have Layer 2-3 switching/routing
capability and are not aware of newly defined service encapsulation
layer. The intent is to identify optimal architecture for flexibly
chaining existing Layer 4-7 functions to meet various service needs.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
Chain Classifier: A component that performs traffic classification
and potentially encodes a unique identifier or the SF MAP Index
introduced by [SFC-Framework] to the packets. The unique identifier
in the packets can be used by other nodes to associate the packets
to a specific service chain and/or steer the packets to the
designated service functions.
DPI: Deep Packet Inspection
FW: Firewall
Layer 4-7 Service Function: Same as the Service Functions defined in
[SFC-Problem] except that they don't have the Layer 2/3 forwarding
capability and are not aware of the new service function header
encapsulations. Many of existing Layer 4-7 service functions fall
into this category. Exemplary functional modules include Firewall,
Deep Packet Inspection (DPI), Encryption, Packet De-duplication,
Compression, TCP Acceleration, NAT, and etc
Layer 4-7 service functions can be instantiated on a standalone
physical or virtual device, which is called "Service Node" by [SFC-
Problem]. Layer 4-7 functions can also be embedded in another
device, such as router/switch or other devices.
SFIC: Service Function Instance Component. One service function
(say, NAT44) could have two different service function
instantiations, one that applies policy-set-A (NAT44-A) and other
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that applies policy-set-B (NAT44-B). There could be multiple
"entities" of NAT44-B (e.g. one "entity" only has 10G capability),
and many "entities" of NAT44-B. Each entity has its own unique
address. The "Entity" in this context is called "Service Function
Instance Component" (SFIC).
3. Legacy Layer 4-7 Service Functions and Chaining
Legacy Layer 4-7 service functions are the existing service
functions that don't have Layer 2/3 forwarding capability and may
not be aware of any new service encapsulation layers or overlay
encapsulation layer being discussed in SFC WG.
3.1. Layer 4-7 Service Functions
A Layer 4-7 service function performs certain action to the packets
belonging to an end-to end flow. The implementation of such service
function can be either Proxy based or Packet Based, or a hybrid of
both when more than one function is performed to the same packet
flow. Multiple service functions can be instantiated on a single
service node as defined by [SFC-ARCH], or embedded in a L2/L3
network node.
o Proxy based service functions: these service functions terminate
original packets, may reassemble multiple packets, reopen a new
connection, or formulate new packets based on the received
packets.
o Packet based service functions: these service functions maintain
original packets, i.e. they don't make changes to packets
traversed through except possibly making changes to metadata
attached to the packet or the packet's outer header fields.
Some Layer 4-7 service functions might have intelligence to choose
different subsequent service functions and pass data packets
directly to the selected service functions. However, most existing
Layer 4-7 service functions don't have this capability.
3.2. Service Functions Chaining for Wireless network
[SFC-MobileNetwork] and [SFC-use-cases] have provided examples of
service chain in mobile network. In particular, the P-GW/PCEF (per
3GPP terminology) determines the desired service treatment, i.e.
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desired sequence of service functions, to specific flows based on
the policies from PCRF.
The P-GW in the figure acts as the Service Chain Classification
Node. P-GW separates the traffic into different categories (or
flows) based on the policies from PCRF. The traffic in each category
(or flow) is mapped to a unique interface (a physical or virtual
port) or a tunnel that is connected to the needed sequence of
service functions.
| Mobile backhaul Network
+-----+ | +---+---+
|PCRF | | |Network|
| | < ---- > |Ctrller|
+-----+ | +----+--+
| |
| |
+---------+ | +--------+ +----+ +---------+
-- >| P-GW | --> |LB |---| FW |--> | Web | ------>
| | | | | | | | Proxy |
--->| | | +--------+ +----+ +---------+
--->| | | +---------+ +----+
-- >| | --> |Video |---| FW |--> ----------- ------>
| [PCEF]| | |Optimizer| | |
| | | +---------+ +----+
--->| | | +--------+ +-----+
-- >| | --> |SBC |---| ACL |--> ----------- ------>
| | | | | | |
+---------+ | +--------+ +-----+
Figure 1 Service Chain for Mobile Network
Here are some of the issues of service chain in wireless network:
o large number of permutations of service functions to be chained
together
o The sequence of services functions applied to selective flows can
change. Sometimes, the change may be triggered by some service
functions on the chain, e.g. DPI. New service functions may need
to be inserted; existing service functions may need to be removed
or changed.
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o The criteria for applying service functions can take combination
of application classification, packet headers, and/or other
factors. For example, the factors that have direct association
with the packet flow include packet source address, destination
address, TCP ports. The factors that do not have association with
the packet flow include user/source location, account status,
time of day, network condition, and etc.
4. Architecture for Chaining Legacy Layer 4-7 Service Functions
4.1. Service Function Forwarder for Layer 4-7 Service Functions
For chaining together legacy Layer 4-7 service functions, the
Service Function Forwarder (SFF) defined by [SFC-Arch] has to be a
separate entity. The SFF can terminate service layer encapsulation
on behalf of service functions/nodes that are not aware service
layer encapsulation. There can be multiple SFF nodes in the Service
Chain domains [SFC-Framework].
Even though Layer 4-7 Service functions can be instantiated
anywhere, it is not uncommon to have multiple service functions
instantiated on nodes in close vicinity to a Service Function
Forwarder node. The following figure depicts the architecture for
chaining those Layer 4-7 service nodes that are not aware of service
layer encapsulation. Each SFF is responsible for forwarding the
traffic to their designated local service functions and for
forwarding the traffic to the next hop SFF after the local service
functions treatment.
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|1 ----- |n |21 ---- |2m
+---+---+ +---+---+ +-+---+ +--+-----+
| Ad | |Content| |Video| |Security|
|Insert | | Opt | | Opt | | App |
+---+---+ +---+---+ +--+--+ +--+--+--+
: : : : :
: : : : :
\ / \ /
+--------------+ +--------+ +---------+
-- >| Chain | ->| SFF |---------> | SFF | ---->
|classifier | |Node-1 | | Node-i |
+--------------+ +----+---+ +----+--+-+
|-- | |
V +--->
+--------+
| SN |
| -j |----->
+--------+
Figure 2 Chaining existing Layer 4-7 service nodes
The "Chain Classifier" node in the figure is to classify the
traffic, encode a unique SF MAP Index [SFC-Framework] to packets or
encapsulate the packets with the SFC header.
The forwarding policies for data packets received by the SFF Nodes
can be carried by the SFC header in the data packets or separate
out-of-band messages from Chain Classier or external controllers.
The SFF nodes can be standalone devices, or can be embedded within
network forwarding nodes. Overlay tunnels are expected to connect
the "SFF nodes" together.
4.2. L4-L7 nodes connection to SFF Nodes
L4-L7 Service nodes can be connected to SFF nodes in various ways.
The topology could be bump in a wire or one armed topology.
o A service function can be embedded in a SFF node (i.e. embedded
in a router or a switch). In this case, the combined entity forms
the SF node described in the [SFC-ARCH].
o A service node can be one hop away from a SFF node
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The one hop between the SFF node and the service node can be a
physical link (e.g. Ethernet link). Under this scenario, there
would be a Link Header, i.e. an outer MAC header, added to the
data packets that meet the steering criteria.
The one hop link can be a transparent link, i.e. no link address
is added to the data packets on the link between the SFF node and
Service node. I.e. the service nodes can apply treatment to data
frames arrived at the ingress port regardless of the Link
Destination address.
o A service node can be multiple hops away, such as when a service
function is deployed in an on-net or private *aaS offering. Under
this scenario, a tunnel is needed between the service node and
the SFF node.
4.3. Traffic Steering at SFF Nodes
The forwarding (or steering) policies for data packets received by
the SFF Nodes can be carried by the SFC header in the data packets
or via separate out-of-band messages from external controller(s) or
the Chain Classifier. When using the out-of-band messages to carry
the steering policies to SFF nodes, the Chain ID (or the SF Map
Index) in the data packet is used to correlate the steering policies
for the data packets.
It worth noting that for one SFF node with multiple Service
Functions (SF) attached, there could be two different Chains going
through one common SF#1, but the Chain #1 needs to go to SF#4 after
SF#1, and the Chain #2 needs to go to another SFF node after the
SF#1. The SFF node has to re-classify traffic coming back from a
port connected to a SF if the Chain ID is not passed by the SF node.
The policies to steer traffic to their corresponding service
functions or service function instances can change. Those steering
policies can be dynamically updated by SFC Header or the out-of-band
messages.
Some service chains may require steering traffic to their
corresponding Layer 4-7 functions based on Layer 1 (e.g. ingress
port), Layer 2 or 3 fields of the data packets. Some service chains
may require steering traffic to their Layer 4-7 service functions
based on some higher layer fields in the data packets, i.e. Layer 4
to Layer 7 fields.
There are multiple types of traffic steering:
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o Fixed header based forwarding: traffic steering based on header
fields that have fixed position in the data packets:
o Forwarding based on Layer 2-3 header fields, such as MAC or
IP Destination Address, Source Addresses, MPLS label, VLAN
ID, or combination of multiple Layer 2-3 header fields.
o Forwarding based on Layer 4 header (TCP or UDP).
o QoS header based forwarding.
o Layer 7 based forwarding: traffic steering (or forwarding) based
on the payload (L7) of data packets.
Multiple data packets may carry some meaningful data, like one
HTTP message. Under this scenario, multiple data packets have to
be examined before meaningful data can be extracted for making
Layer 7 based forwarding decision.
o Metadata based steering: traffic steering (or forwarding) based
on the identity of the initiating user, the UE model or type, the
site name or FQDN, or network conditions (congestion,
utilization, etc.).
However those metadata might not necessarily be carried by each
data packet due to extended bits required that can cause high
probability of packet fragmentation. Those metadata can be
dynamically passed down to steering nodes in some forms of
steering policies from network controller(s).
5. Control Plane for L4-L7 Service Function Chain
5.1. Multiple Instances of a Service Function
One service function (say, NAT44) could have two different service
function instantiations, one that applies policy-set-A (NAT44-A) and
other that applies policy-set-B (NAT44-B). There could be multiple
"entities" of NAT44-B (e.g. one "entity" only has 10G capability),
and many "entities" of NAT44-B. Each entity has its own unique
address (or Locator in draft-parker-sfc-chain-to-path). The "Entity"
in this context is called "Service Function Instance Component"
(SFIC).
It is not uncommon to have multiple SFICs with some in close
proximity and others far apart being attached to different Service
Function Forwarder (SFF) nodes. In Network Function Virtualization
(NFV) environment, there could be very large number of SFICs for
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each service function. NFV imposes higher chance of state or
attachment change for SFICs due to virtual instances'
creation/deletion/migration.
At functional level, the order of service functions, e.g. Chain#1
{s1, s4, s6}, Chain#2{s4, s7}, is important, but very often which
SFIC of the Service Function "s1" is selected for the Chain #1 is
not. It is also possible that multiple SFICs of one service function
can be reached by different network nodes. The actual SFIC selected
for a service chain is called "Service Chain Instance Path".
There are various policies that could be employed to select SFIC for
service chain instance path. The SFC WG should stay away from or
open to all possible ways of specifying the way policy decisions are
performed.
Some Service Chain Classifier can specify exact service chain
instance path. Under other scenarios where there is large number of
SFICs per function, it should be acceptable for Service Chain
classifier to only identify the chaining at function level and have
another entity managing the detailed service instance path.
When there is change to SFIC selected for a Service Chain Instance
Path, either in-band or out-of-band messages can be sent to the SFF
nodes to update the steering policies dynamically.
The downside with out-of-band messages is synchronization and race
conditions. For a newly recognized flow, it is not scalable to
expect the classifier node to queue the packets until the out-of-
band notification is acknowledged by every Service Function
Forwarder node. On the other hand, it is reasonable to use out-of-
band messages to inform forwarding policies on SFF nodes if the
forwarding policies can be pre-established before traffic arrives at
the Classifier nodes, e.g. subscriber profile basis service chain
instance path.
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|
+---+------+ +---+---+ +--+-----+
|controller| |Service| |Service |
| | |Func-1 | |Func- m |
+---+------+ +----+--+ +--+--+--+
/ \ \ : /
/ \ +---------------+ : /
/ \ \ : /
+-----------+ +--------+ +---------+
-- >|Classifier | --> |SFF |------> | SFF | ------>
| node | |Node-1 | | Node-2 |
+-----------+ +--------+ +---------+
Figure 3 Controller for Service Chain Instance Path
Some service functions make changes to data packets, such as NAT
changing the address fields. If any of those fields are used in
traffic steering along the service chain, the criteria can be
different before and after those the service functions.
5.2. Service Chain Classification
The policy for associating flows with their service chains can be
complicated and could be dynamic due to different behavior
associated with chains, balancing load among multiple instances for
one service function, and instance failure.
For a chain of {FW, Header_enrichment, smart_node, Video_opt,
Parental Control}, the video optimizer really needs to work on the
response path. It may also use completely different encapsulation
e.g. ICAP for example. There could be Smart-Node to further classify
a particular part of the flow and bypass something, say the
video_opt. Therefore, the classification done by the service chain
classification nodes at the network entrance can't completely
dictate the exact sequence of service functions.
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+-------------------+
|Chain Orchestration|
| |
+-------------------+
|
| +------------+
| <------------------------|Chain Adjust|
| | | Entity |
| | +------------+
| | / \
| V / \
+---+------+ +---+---+ +--+-----+
|controller| |Service| |Service |
| | |Func-1 | |Func- m |
+---+------+ +----+--+ +--+--+--+
/ \ \ : /
/ \ +---------------+ : /
/ \ \ : /
+-----------+ +--------+ +---------+
-- >|Classifier | --> |SFF |------> | SFF | ------>
| node | |Node-1 | | Node-2 |
+-----------+ +--------+ +---------+
Figure 4 Service Chain Re-classificaiton
The Service Chain Classification node can encounter flows that don't
match with any policies. There is a default policy that applies all
statutorily required policies to the unknown flows.
Multiple flows can share one service chain. The criteria to select
flows to be associated with their service chain could be different.
For example, for one service chain "A" shared by Flow X, Y, Z:
o Criteria for Flow X to the Service Chain "A" are TCP port
o Criteria for Flow Y to the Service Chain "A" are Destination
Address
o Criteria for Flow Z to the Service Chain "A" are MPLS label.
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5.3. Layer 4-7 traffic Steering
Very often the criteria for steering flows to service functions are
based on higher layer headers, such as TCP header, HTTP header, etc.
Most of deployed switches/routers are very efficient in forwarding
packets based on Layer 2 or Layer 3 headers, such as MAC/IP
destination addresses, or VLAN/MPLS labels but have limited capacity
for forwarding data packets based on higher layer header. As of
today, differentiating data packets based on higher layer headers
depends on ACLs (Access Control List field matching) or DPI, both of
which are relatively expensive and extensive use of such facilities
may limit the bandwidth of switches/routers.
The Service Chain classification node introduced by [Boucadair-
framework] and [SFC-ARCH] can alleviate the workload on large number
of nodes in the network, including SFF nodes, from steering traffic
based on higher layer fields.
|1 ----- |n |21 ---- |2m
+---+---+ +---+---+ +-+---+ +--+-----+
| Ad | |Content| |Video| |Security|
|Insert | | Opt | | Opt | | App |
+---+---+ +---+---+ +--+--+ +--+--+--+
: : : : :
: : : : :
\ / \ /
+--------------+ +--------+ +---------+
- >| Chain | ->| SFF |--------> | SFF | --->
|classification| |Node-1 | | Node-2 |
+--------------+ +--------+ +---------+
Figure 5 Service Chain Marking At Ingress
A Service Chain Classification node can associate a unique Service
Chain Label (e.g. Layer 2 or 3 Label) or SF MAP Index to the packets
in the flow. Such a Layer 2 or 3 Label makes it easier for
subsequent nodes along the flow path to steer the flow to the
service functions specified by the flow's service chain.
The network elements that have the Service Chain Classification
Function are most likely network ingress edge nodes, such as
Wireless Packet Gateway, Broadband Network Gateways, Cell Site
Gateways, etc.
In some situations, like service chain for wireless subscribers,
many flows (i.e. subscribers) have common service chain
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requirements. Under those situations, the Service Chain
classification Functional can mark multiple flows with the same
service chain requirement using the same Layer 2 or 3 Label, which
effectively aggregates those flows into one service chain.
For service chains that are shared by a great number of flows, they
can be pre-provisioned. For example, if VLAN ID=10 is the service
chain that need to traverse "Service-1" at SFF Node #1 and "Service-
3" at SFF Node #2, the steering policy for VLAN ID=10 can be
dynamically changed by controllers.
6. Service Chain from the Layer 7 Perspective
From the Layer 7 perspective, the service chain can be much more
complex. As shown in the figure below, the service functions to be
chained can depend on the HTTP message request and reply. The
service chain classification nodes may have to examine the whole
HTTP message to determine the specific sequence of service functions
for the flows. The HTTP message might have to be extracted from
multiple data packets. Sometimes, the logic to steer traffic to
chain of service functions might depend on the data retrieved from a
database based on messages constructed from packets. The decision
may depend on the HTTP response rather than the request, or it may
depend on a particular sequence of request-response messages. The
message handler may also alter the Layer 7 service chain based on
hints or modification done by previous service function. HTTP based
service function may insert HTTP header to add further criterion for
service selection in the next round of classification.
+----------+
Client --------->( Layer 7 )---------> Internet
<---------( Message )<---------
( Handler )
--------( )--------________
/ +----------+ \
/ / \ \
|1 |2 |3 |4
+---+---+ +---+---+ +-+---+ +--+-----+
| Ad | |Content| |Video| |Security|
|Insert | | Opt | | Opt | | App |
+---+---+ +---+---+ +--+--+ +--+--+--+
: : : : :
: : : : :
Figure 6 Layer 7 Service Chain Complexity
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7. Conclusion and Recommendation
There are many service functions being deployed already in the
network. Many of them are not capable to adapt to new service chain
encapsulation layer.
This document provides architecture framework for chaining those
Layer 4-7 service functions that are not aware of new service layer
encapsulation.
8. Manageability Considerations
There currently exists no single management methodology to control
the L2-4 packet-based forwarding device, the L4-7 service delivery
device, and the L7+ application server. Such unified management of
configuration state is required for service function chaining to be
a practical solution.
9. Security Considerations
TBD
10. IANA Considerations
This document requires no IANA actions. RFC Editor: Please remove
this section before publication.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
11.2. Informative References
[Boucadair-framework] M. Boucadair, et al, "Differentiated Service
Function Chaining Framework", < draft-boucadair-service-
chaining-framework-00>; Aug 2013
[SFC-Problem] P. Quinn, et al, "Service Function Chaining Problem
statement", <draft-quinn-sfc-problem-statement-02>, Dec 9,
2013
[SFC-Framework] M. Boucadair, et al, "Service Function Chaining:
Framework & Architecture", < draft-boucadair-sfc-
framework-00>; Oct 2013
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[SFC-Arch] P. Quinn, et al, "Service Function Chaining (SFC)
Architecture", < draft-quinn-nsc-arch-04>, Jan 2014.
[NSH-Header] P. Quinn, et al, "Network Service Header", < draft-
quinn-nsh-01>, July 12, 2013
[SC-MobileNetwork] W. Haeffner, N. Leymann, "Network Based Services
in Mobile Network", IETF87 Berlin, July 29 2013
[Application-SDN] J. Giacomonni, "Application Layer SDN", Layer 123
ONF Presentation, Singapore, June 2013
[SC-Use-Case] Liu, et, al., "Service Chaining Use Cases", < draft-
liu-service-chaining-use-cases-00>, Sept, 2013
12. Acknowledgments
This draft has merged some sections from
http://datatracker.ietf.org/doc/draft-parker-sfc-chain-to-path/.
This draft has taken input from "Application Layer SDN" presentation
given by John Giacomoni of F5 at Layer 123 conference. Thanks to
Huang Shi Bi and Li Hong Yu for the valuable comments and
suggestions.
This document was prepared using 2-Word-v2.0.template.dot.
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Internet-Draft Chaining Legacy Layer 4-7 SF February 2014
Authors' Addresses
Linda Dunbar
Huawei Technologies
1700 Alma Drive, Suite 500
Plano, TX 75075, USA
Phone: (469) 277 5840
Email: ldunbar@huawei.com
Ron Parker
Affirmed Networks
Acton, MA 01720
USA
Email: ron_parker@affirmednetworks.com
Ian Smith
F5 Networks
Email: I.Smith@F5.com
Sumandra Majee
F5 Networks
Email: S.Majee@F5.com
Ning So
Tata Communications
Email: Ning.So@tatacommunications.com
Donald Eastlake
Huawei Technologies
155 Beaver Street
Milford, MA 01757 USA
Phone: 1-508-333-2270
Email: d3e3e3@gmail.com
Dunbar, et al. Expires August 10, 2014 [Page 17]