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VPN model that allows other service
providers or corporate customers to
interconnect their own IP/MPLS networks
over Telkom’s MPLS backbone. This
eliminates the need for customer carriers
and service carriers to build and maintain
their own MPLS backbone. In the
backbone, the CsC concept provides
complete separation of the different service
carriers’ traffic.
A Service Carrier is a collection of
Service (or customer-specific) Provider
Edge routers (S-PEs), essentially forming a
layer around the Backbone Carrier
network. Service Carriers also include their
respective Customer Edge (CE) routers.
S-PE and CE routers can only belong to a
single Service Carrier at any one time.
In essence, IPNet will consist of a
Backbone Carrier, supporting various
Service or Customer Carriers each
retaining a level of autonomy (e.g. security,
management, Quality of Service
implementation) from the core. At a basic
technical level, it means that any number of
customer VPNs are embedded and treated
as a single VPN within the backbone
carrier infrastructure by means of multiple
stacked MPLS labels, while preserving the
customer’s unique parameters, such as
Quality of Service models.
Network resilience
Telkom’s networks are generally viewed as
three layers, ie access, edge and core.
The different network elements are
interconnected utilising Synchronous Digital
Hierarchy (SDH), with the primary physical
interconnecting medium being fibre.
The transport network equipment is
connected in a mesh or ring topology,
providing for redundancy. To further
improve resilience, intelligent ASTN
switches are deployed in the long haul
network to provide automatic provisioning,
routing, and restoration capability.
Generally, at the access, no resilience is
present in the network architecture towards
the edge other than physical protection
at the SDH layer where end-to-end path
protection, utilising 1+1 protection
architecture, i.e. a working path and a hot
standby
deployed.
protection path, has been
The traffic leaving or entering edges to or
from the network is protected in the core.
Core redundancy provides protection in
edge to edge and edge to international
destination set-ups. The degree of
redundancy varies across the different
technologies and networks.
Voice network
Dual connectivity exists between edge to
core nodes and core to international
gateway nodes. The transmission links
between the edge and the core pair nodes
are geographically separated. These links
are protected to eliminate any single point
of failure in the transport network. All links
are designed to cater for the busy hour
loads and have been implemented in a
50:50 load sharing fashion with each
route limited to 80% utilisation.
In the event of a failure of an international
gateway during the peak hour, about 38%
of the international traffic will be lost. In the
event of a failure of a core switch during
the peak hour, about 38% of national and
international traffic will be lost from the
secondary layer of a particular region.
Activation of disaster recovery procedures
and plans to re-route traffic will further limit
the loss of traffic. The Intelligent Network
platforms, providing advance services,
cater for protection of traffic under failure
conditions.
Signalling
No risk exists from a national perspective
as full redundancy has been implemented.
Due to the fact that the international
Signalling Transit Points are not connected
as a mated pair to all international
destinations, failure of an international
gateway Signalling Transit Point may
result in the loss of some international
connections.
Telkom Annual Report 2009 99
Data networks
At the core layer and between the core
and the edge nodes, full resilience exists.
Edge devices are connected to two core
devices, located in physically diverse
buildings. The connectivity between the
edge and each core router as well as the
core infrastructure is dimensioned to carry
the full traffic load in the event of a link
failure or core node failure. Edge to core,
inter-core and edge to International
destinations are therefore fully redundant.
Connectivity to international destinations is
provided from two physically diverse
nodes, through different cable landing
stations and different submarine cable
networks to multiple international nodes on
different continents that are all
interconnected using protected or
restorable transmission systems. In the event
of the loss of one of the local nodes,
potentially 38% of the IP throughput traffic
could be lost. Mechanisms will schedule
traffic and prioritisation of traffic will
take place.
Service level agreements are offered to
clients to provide improved resilience from
the customer site to the edge.
Power
Only 12V and 48V direct current (DC)
equipment is utilised. Some alternating
current (AC) equipment is used, mainly in
the server environments, eg data centres
and at sites where DC is not available, eg
at customer service branches.
Operations centres, Core nodes, Edge
nodes, International gateway nodes and
any station carrying core or edge traffic
have been defined as critical sites where a
disruption of service cannot be tolerated.
Power availability is ensured, using a
combination of battery back up and AC
standby plants.
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