5.3 Core Network Functions Virtualization: vEPC 135
An edge pointing from one node ⟨H 1 , D 1 , S 1 ⟩ to another ⟨H 2 , D 2 , S 2 ⟩
means when a packet in H 1 arrives at D 1 with state S 1 , it will be
modified to H 2 and forwarded to a device D 2 at state S 2 . If the device
D 1 does not modify the packet header, then H 1 is equal to H 2 . If the
packet H 1 does not trigger the state transition, then S 1 is equal to
S 2 . Figure 5.14 shows an example of a path of packets H 1 traversing
through D 0 , D 1 , and D 2 .
Essentially, an SFG edge can represent one of two events: (1) a
packet is modified and forwarded to next hop or dropped; (2) a device
is changing its state to the next state. Accordingly, we use two different
types of edges to represent the different events.
Using the SFG, we develop a verification algorithm that is capable of
verifying the dynamic and stateful behavior of the network. The verification leverages the structure of our NF abstract model, namely due
to the use of state machine, for each flow the NF will be in one and only
one state at any given time. Essentially, only one node in an NF’s state
will be active. By activating different nodes (corresponding to different
states of an NF) during the verification process, we are able to verify
different forwarding scenarios across NFs and states.
5.3 Core Network Functions Virtualization:
vEPC
The 3G packet core (PC) network consist of three interacting
domains: core network (CN), 3G PC terrestrial radio access network
(UTRAN), and UE. The main function of the core network is to
provide switching, routing, and transit for user traffic. Core network
also contains the databases and network management functions. It is
the common packet core network for GSM/GPRS, WCDMA/HSPA,
and non-3GPP mobile networks. The packet core system is used for
transmitting IP packets.
The core network is divided into circuit- and packet-switched
domains. Some of the circuit-switched elements are mobile switching
center (MSC), visitor location register (VLR), and gateway MSC.
Packet-switched elements are SGSN and GGSN. Some network elements such as EIR, HLR, VLR, and AUC are shared by both domains.
The architecture of the core network may change when new services
and features are introduced. Number portability database (NPDB)
will be used to enable user to change the network while keeping their
An edge pointing from one node ⟨H 1 , D 1 , S 1 ⟩ to another ⟨H 2 , D 2 , S 2 ⟩
means when a packet in H 1 arrives at D 1 with state S 1 , it will be
modified to H 2 and forwarded to a device D 2 at state S 2 . If the device
D 1 does not modify the packet header, then H 1 is equal to H 2 . If the
packet H 1 does not trigger the state transition, then S 1 is equal to
S 2 . Figure 5.14 shows an example of a path of packets H 1 traversing
through D 0 , D 1 , and D 2 .
Essentially, an SFG edge can represent one of two events: (1) a
packet is modified and forwarded to next hop or dropped; (2) a device
is changing its state to the next state. Accordingly, we use two different
types of edges to represent the different events.
Using the SFG, we develop a verification algorithm that is capable of
verifying the dynamic and stateful behavior of the network. The verification leverages the structure of our NF abstract model, namely due
to the use of state machine, for each flow the NF will be in one and only
one state at any given time. Essentially, only one node in an NF’s state
will be active. By activating different nodes (corresponding to different
states of an NF) during the verification process, we are able to verify
different forwarding scenarios across NFs and states.
5.3 Core Network Functions Virtualization:
vEPC
The 3G packet core (PC) network consist of three interacting
domains: core network (CN), 3G PC terrestrial radio access network
(UTRAN), and UE. The main function of the core network is to
provide switching, routing, and transit for user traffic. Core network
also contains the databases and network management functions. It is
the common packet core network for GSM/GPRS, WCDMA/HSPA,
and non-3GPP mobile networks. The packet core system is used for
transmitting IP packets.
The core network is divided into circuit- and packet-switched
domains. Some of the circuit-switched elements are mobile switching
center (MSC), visitor location register (VLR), and gateway MSC.
Packet-switched elements are SGSN and GGSN. Some network elements such as EIR, HLR, VLR, and AUC are shared by both domains.
The architecture of the core network may change when new services
and features are introduced. Number portability database (NPDB)
will be used to enable user to change the network while keeping their