As wireless operators deploy packet-based networks including LTE technology, considerations for the network layout, or topology, are changing. LTE has its own topology changes, but another point of debate within networks are whether to go with a Carrier Ethernet architecture or an MPLS topology.
COMMON NETWORK TOPOLOGIES
Within telecom networks, there are multiple topologies to consider in terms of which topologies best serve network needs. Some of the basic network topologies are: ring, star (point-to-multi-point), tree (hierarchical), ladder, bus and so on. The most common topologies for radio networks are ring and tree, or a combination of both, according to a report by Ceragon (1). In a tree topology, “fewer links can cause major network failures, and only those links require protection schemes. Alternatively, closing the chain yields the ring, which is the most efficient topology in terms of protection.”
Both ring and tree topologies have competing advantages and disadvantages in terms of availability, resiliency, latency, capacity, scalability and capital costs. According to Ceragon, “There is no single ‘correct’ topology. Network planners should consider the relevant environmental and business conditions (such as available spectrum, and radio and antenna costs), reliability requirements, and application characteristics, in order to determine the best solution for their needs.”
Some of these basic architectures are illustrated below.
PHYSICAL AND LOGICAL MPLS TOPOLOGY
There are both physical and logical topologies to consider. Physical network topology encompasses the relationships between the physical locations of various pieces of network equipment. There is also the logical network topology, or how those network elements communicate with each other.
As telecom networks expand to encompass a broader use of LTE, their topology also can change due to communication features in the new standards. The implementation of X2 traffic between smarter cellular base stations means that cell sites can communicate with one another to apply network intelligence, rather than only communicating with the network core. This is a significant change from earlier generations of technology.
More importantly for overall network topology, though, is that network operators are moving toward extending the use of packet-based technology within the network.
“Obviously, LTE is packet-based,” said Esteban Monturus, backhaul market analyst for telecom research firm Maravedis Inc. “When you migrate to a packet-based network, you have different flavors or strains in the industry. Ethernet has been the most common technology at the beginning, because it’s more common, and it is well-known because of the number of years it has been used. But … MPLS is getting more and more attention from the industry.”
Monturus said that operators who have opted to use MPLS as their choice for a packet-based core network are now exploring the expansion of MPLS topology to their access and aggregation networks, in order to have a single technology to manage.
“So here you have a battle between Carrier Ethernet and MPLS as the main technology for backhaul,” he said. “I think it really depends on the topology that the operator has deployed.”
If an operator has many point-to-point links and microwave links, “deploying MPLS in such a simple topology, like a tree, doesn’t provide many advantages,” Monturus said.
“When you have rings or meshed backhaul in the access and aggregation, it is more suitable for thinking about MPLS, because the capabilities of MPLS in terms of protection and also load-balancing of traffic. Then you can really take advantage of those features.”
Operators who are deploying LTE on a small scale may not tweak their backhaul networks accordingly. But operators like Verizon Wireless and AT&T, who are aggressively rolling out the faster LTE networks, “wouldn’t be able to cope without really advanced backhaul networks,” Monturus added.
He also noted that the choice of Carrier Ethernet architecture currently does not preclude an operator from opting for MPLS topology at a later time.
Additional sources:
1.Ceragon white paper, Wireless Backhaul Topologies: Analyzing Backhaul Topology Strategies. http://www.ceragon.com/files/Ceragon_Wireless_Backhaul_Topologies_%20Tree_vs_%20Ring_%20White%20Paper.pdf
